Preparation Of TiB₂ Absorbent And Its Research On High-temperature Radar Absorbing Material

The rapid development of stealth technology for high-temperature components of weapon equipment had put forward the urgent requirement for high-temperature radar absorbing materials,but the complex high temperature environment made the improvement of high-temperature microwave absorption performance become a great challenge all the time.To obtain the high-temperature microwave absorbing materials with wide application temperature range,enhanced radar wave absorption bandwidth and outstanding temperature stability in absorption performance,this paper investigated the TiB₂ absorbent and high-temperature radar absorbing materials.This work analyzed the dielectric loss property of TiB₂ absorbent,explored the relation among high-temperature electric conductivity,dielectric and microwave absorption properties by preparing composite materials with positive and negative resistance temperature coefficient material,and fabricated the periodic structure using ceramic materials based on the structural design ideas.The main contents and results are shown as follows:TiB₂ was synthesized by the self-propagating high temperature synthesis(SHS)process and carbothermal method,and the relation between the microstructure and dielectric loss characteristic was investigated.TiB₂(S-TiB₂)synthesized by the SHS showed a particle-like morphology;TiB₂(R-TiB₂)synthesized by the carbothermal method performed two microstructures:particles and fibers,and the number of fibers increased followed by a reduction with the lifting synthetic temperature and increased with the holding time.The dielectric constants of S-TiB₂/paraffin and R-TiB₂/paraffin composites increased with the increasing S-TiB₂ and R-TiB₂ contents,respectively;Because R-TiB₂ had stronger polarization loss and conductance loss,R-TiB₂ performed a better dielectric loss characteristic,and it performed enhanced effective absorption bandwidth(4.64 GHz,RL<-10 dB)with the thickness of 1.25 mm.Based on the composite materials with positive and negative resistance temperature coefficient materials,TiB₂/MgO(S-TiB₂/MgO and R-TiB₂/MgO)and TiB₂/Al₂O₃(S-TiB₂/Al₂O₃ and R-TiB₂/Al₂O₃)composites were prepared by the sink plasma sintering(SPS)method,the influences of preparation parameters on dielectric and microwave absorption properties were studied,and their high-temperature electric conductivity,dielectric and microwave absorption properties were analyzed.S-TiB₂ content and sintering temperature had little impact on the dielectric loss performance of ceramics.Both the effective absorption bandwidths(RL<-5 dB)of S-TiB₂/MgO and S-TiB₂/Al₂O₃ ceramics first increased and then decreased with rising S-TiB₂ content,and decreased with lifting sintering temperature.The high-temperature electric conductivity of R-TiB₂/MgO changed a little,but showed a sharp increment for R-TiB₂/Al₂O₃,and their dielectric constants increased with raising measuring temperature.Because R-TiB₂/Al₂O₃ performed higher electric conductivity,but it appeared impedance mismatch under higher temperatures,the microwave absorption property of R-TiB₂/Al₂O₃ was better than that of R-TiB₂/MgO at 25?500?,but microwave absorption property of R-TiB₂/Al₂O₃ was worse than that of R-TiB₂/MgO at800?.To obtain the high-temperature conductivity which matches the high-temperature microwave absorption performance,R-TiB₂/Al₂O₃/MgAl₂O₄ceramics were prepared by SPS,and the influences of R-TiB₂ content on the dielectric and microwave absorption properties were investigated.Meanwhile,the high-temperature electrical conductivity,dielectric and microwave absorption properties of ceramics with different Al₂O₃ content were analyzed.the dielectric loss and the effective absorption bandwidth first increased and then decreased with rising R-TiB₂ content.The electrical conductivity and permittivity slowly grew with the lifting temperature and Al₂O₃ content.Furthermore,due to the compensating effect of the positive and negative resistance temperature coefficient materials on the high-temperature electrical conductivity as well as the co-play of the dipolar and interfacial polarization at elevated temperatures,R-TiB₂/Al₂O₃/MgAl₂O₄ceramics performed obvious temperature stability in microwave absorption performance at 25?700?.Based on the ceramics with slowly increasing high-temperature electric conductivity,combining with the characteristics that S-TiB₂ can be synthesized massively,and hot-pressing sintering process can prepare large-area materials,S-TiB₂/Al₂O₃/MgAl₂O₄ ceramics were prepared by the hot-pressing sintering process with S-TiB₂,Al₂O₃ and MgO as raw materials,and the periodic structure was designed using S-TiB₂/Al₂O₃/MgAl₂O₄ ceramics as pattern layer(square structure)and dielectric layer based on the structural design ideas.Both the S-TiB₂ content,the structure parameter of the pattern layer and the dielectric layer could play key roles in microwave absorption.At the temperature of 25?700?,when the S-TiB₂content,the side length and thickness of square structure(a and d₂),and the thickness of the dielectric layer(d₃)were 18 wt%,9 mm,4.4 mm and 1.2 mm,respectively,the effective absorption bandwidth could cover the whole frequency band of 8.2?18 GHz(RL<-5 dB).Besides,the measured high-temperature microwave absorption of the periodic structure met its calculated microwave absorption,and it had satisfying high temperature microwave absorption at 1100?,performing characteristics of wide application temperature range,enhanced radar wave absorption bandwidth and outstanding temperature stability in absorption performance.